It's entirely possible--I wouldn't say common, but in my experience from talking to people it happens to a lot of guys at least once.
For one thing, orgasm and ejaculation are two different things. They very, very often go together in men, but they don't have to. It is possible to orgasm and not ejaculate.
Thing two is something called retrograde ejaculation, in which the semen actually goes into the bladder instead of out of the urethra. If the guy pees afterward this can make his urine cloudy.
Neither thing is harmful, though they can be a little discombobulating, I'd think. No big deal, though.
And when her spirit left her body/How it split the sun/I know that she will live forever/All goes on and on./And she goes/And now she knows she'll never be afraid... - Neutral Milk Hotel